This project encompasses all statistical coordinating center responsibilities for collaborative clinical studies undertaken by this Section and the Office of the Chief. A major initiative involves the study of the etiology of Parkinson's disease (PD) using the twin pair registry of the National Academy of Sciences/National Research Council. The prevalent cases of PD in the more than 6,000 twin pairs in which both members are alive, will be identified. This observational study will establish: environmental, medical and family histories of both affected and unaffected members of the twin pairs; DNA banking; and measurement of progression of disease over time. This project will investigate genetic and environmental contributions and their interactions to the etiology of PD. A Cooperative Agreement has been funded for the clinical aspects of this study. BFSB is acting as the statistical coordinating center. The study is ongoing. A second collaborative project involves a two-phase prevalence survey of major neurologic disorders in Junin, a city of about 70,000 inhabitants, in the Province of Buenos Aires, Argentina. This household survey, funded by the Fundacion para la Investigacion en Neuroepidemiologia , is one of the largest of its kind in Latin America. On the basis of a two-stage systematic sample of households, 17,049 persons from 5,648 households were screened in phase 1, to identify those persons who possibly had a disorder of interest. In phase 2, the 817 persons screened as positive were evaluated (usually by means of a clinical examination) by neurologists using established diagnostic criteria. BFSB has collaborated on the design and data collection for this study, and is now collaborating on the data analysis and preparation of reports.